Petroleum resid is the bottoms or heavy fraction produced by distilling petroleum crudes and may be referred to as atmospheric resid and vacuum resid to indicate the type of distillation. Resid may be converted into transportation fuels such as jet, diesel, and gasoline by a variety of processes. However, the metal content of the resid, e.g., alkali, alkaline earth metals, first transition metals, as well as Al, Sn, Pb, Sb, and the like may poison the catalysts used and cause higher coke production, which can decrease the conversion and/or selectivity of the various processes employed.
Conventionally, the resid metal content may be concentrated in a coke or bottoms product of thermal processes such as coking and visbreaking, which also produce lighter hydrocarbon fractions such as naphtha, diesel. Although the metals are concentrated in the heavier products in these thermal processes, the lighter products may require additional or specialized processing because they contain significantly more metals relative to similar boiling range straight run fractions. Metals in resid may also be removed by adsorption onto solid particles such as catalysts or adsorbents. Such particles may be used in conjunction with resid hydrotreating processes that also reduce the nitrogen and sulfur content of the resid.
Various processes using ionic liquids to remove sulfur and nitrogen compounds from hydrocarbon fractions are known. U.S. Pat. No. 7,001,504 B2 discloses a process for the removal of organosulfur compounds from hydrocarbon materials which includes contacting an ionic liquid with a hydrocarbon material to extract sulfur containing compounds into the ionic liquid. U.S. Pat. No. 7,553,406 B2 discloses a process for removing polarizable impurities from hydrocarbons and mixtures of hydrocarbons using ionic liquids as an extraction medium. U.S. Pat. No. 7,553,406 B2 also discloses that different ionic liquids show different extractive properties for different polarizable compounds.
Liquid/Liquid Extraction of Metal Ions in Room Temperature Ionic Liquids, by Visser, Ann E., et al, SEPARATION SCIENCE AND TECHNOLOGY, 36(5&6), 785-804, (2001), Marcel Dekker, Inc., discloses the use of room temperature ionic liquids, specifically, 1-alkyl-3-methylimidazolium hexafluorophosphate, to separate metal ions from aqueous solutions.
There remains a need in the art for improved processes that reduce the metal content of petroleum resid.